I. Field of the Invention
The present invention relates to the treatment of vascular disease, and more particularly to a vascular filter system for use during medical procedures.
II. Discussion of the Related Art
Percutaneous transluminal coronary angioplasty (PTCA), stenting and atherectomy are therapeutic medical procedures used to increase blood flow through the coronary arteries. These procedures may often be performed as alternatives to coronary bypass surgery. Percutaneous transluminal angioplasty (PTA) and stenting may often be performed as alternatives to carotid endarterectomy, and femoral-popliteal bypass procedures. In PTCA or PTA procedures, the angioplasty balloon is inflated within the stenosed vessel, at the location of an occlusion, in order to shear and disrupt the wall components of the vessel to obtain an enlarged lumen. In stenting, an endoluminal prosthesis is implanted in the vessel to maintain patency following the procedure. In atherectomy, a rotating blade is used to shear plaque from the arterial wall.
One of the potential complications associated with all these techniques is the accidental dislodgment of plaque, thrombus or other embolic particulates generated during manipulation of the vessel, thereby potentially causing occlusion of the narrower vessels downstream and ischemia or infarct of the organ which the vessel supplies. Such emboli may be extremely dangerous to the patient, and may result in myocardial infarction, stroke or limb ischemia. In 1995, Waksman et al. disclosed that distal embolization is common after directional atherectomy in coronary arteries and saphenous vein grafts. See Waksman et al., American Heart Journal 129(3): 430–5 (1995). This study found that distal embolization occurs in twenty-eight percent (31 out of 111) of the patients undergoing atherectomy. In January 1999, Jordan, Jr. et al. disclosed that treatment of carotid stenosis using a percutaneous angioplasty with stenting procedure is associated with more than eight times the rate of microemboli seen using carotid endarterectomy. See Jordan, Jr. et al., Cardiovascular Surgery 7(1): 33–8 (1999). Microemboli, as detected by transcranial Doppler monitoring in this study, have been shown to be a potential cause of stroke. The embolic materials include calcium, intimal debris, atheromatous plaque, and thrombi.
In order to initiate these procedures, one must first introduce a guidewire into the lumen of the vessel to serve as a conduit for other interventional devices, such as angioplasty balloons and stent delivery systems. This guidewire must be advanced into a position past the location of the occlusion. Guidewires must be capable of traversing tortuous pathways within the body, consisting of bends, loops and branches. For this reason, guidewires need to be flexible, but they should also be sufficiently stiff to serve as conduits for other devices. In addition, they must be “torqueable” to facilitate directional changes as they are guided into position.
Guidewires are well known in the art, and are typically made of stainless steel, tantalum or other suitable materials, in a variety of different designs. For example, U.S. Pat. Nos. 4,545,390 and 4,619,274 disclose guidewires in which the distal segment is tapered for greater flexibility. The tapered section may be enclosed in a wire coil, typically a platinum coil, which provides increased column strength and torqueability. Another design is identified in U.S. Pat. No. 5,095,915, where the distal segment is encased in a polymer sleeve with axially spaced grooves to provide bending flexibility.
Vascular filters are also well known in the art, especially vena cava filters, as disclosed in U.S. Pat. Nos. 4,727,873 and 4,688,553. There is also a substantial amount of medical literature describing various designs of vascular filters and reporting the results of clinical and experimental use thereof. See, for example, the article by Eichelter and Schenk, entitled “Prophylaxis of Pulmonary Embolism,” Archives of Surgery, Vol. 97 (August, 1968). See, also, the article by Greenfield, et al., entitled “A New Intracaval Filter Permitting Continued Flow and Resolution of Emboli”, Surgery, Vol. 73, No. 4 (1973).
Vascular filters are often used during a postoperative period, when there is a perceived risk of a patient encountering pulmonary embolism resulting from clots generated peri-operatively. Pulmonary embolism is a serious and potentially fatal condition that occurs when these clots travel to the lungs. The filter is therefore typically placed in the vena cava to catch and trap clots before they can reach the lungs.
Many of the prior art vascular filters are intended to be permanently placed in the venous system of the patient, so that even after the need for the filter has passed, the filter remains in place for the life of the patient. U.S. Pat. No. 3,952,747 discloses a stainless steel filtering device that is permanently implanted transvenously within the inferior vena cava. This device is intended to treat recurrent pulmonary embolism. Permanent implantation is often deemed medically undesirable, but it is done because filters are implanted in patients in response to potentially life-threatening situations.
To avoid permanent implantation where possible, it is highly desirable to provide an apparatus and method for preventing embolization associated with angioplasty, stenting or other procedures. In particular, it is desirable to provide a device which may be temporarily placed within the vascular system to collect and retrieve plaque, thrombus and other embolic particulates which have been dislodged during angioplasty, stenting or other procedures. Such a device is removed at the end of the procedure. U.S. Pat. Nos. 6,179,861 and 6,001,118 disclose guidewire-based filters where the filter resembles a windsock and is supported by one or more articulated support hoops. U.S. Pat. Nos. 5,814,064 and 5,827,324 disclose guidewire-based filter devices, wherein the filter is expanded to a predetermined diameter through the introduction of a fluid or a gas. U.S. Pat. Nos. 6,168,604 and 6,152,946 disclose guidewire-based filters, wherein the diameter of the filter is controlled by advancing and retracting a sheath over the filter component.
One concern commonly encountered with these devices is that the filter is attached to the guidewire, which increases the profile or diameter thereof, making it is difficult to push and track these devices through the vasculature, to reach the treatment site. A related concern commonly encountered with these devices is that if the filter becomes clogged with emboli, such that distal perfusion is no longer possible, the filter must be removed and replaced, thereby losing guidewire position.
The prior art fails to disclose any guidewire-based vascular filters which may be used to address the clinical problems of poor pushability and trackability through the vasculature, and loss of guidewire position upon removal of filters permanently attached to guidewires.